Time delay mercury switch



Feb. 14, 1961 BANKS 2,972,025

TIME DELAY MERCURY SWITCH Filed Sept. 22, 1959 INVEN TOR. WALDO H. BANKS A TTORNEY United States Patent O TIME DELAY MERCURY SWITCH Waldo H. Banks,-.Hopedale, Mass., assignor to Draper Corporation, Hopedale, Mass., a corporation of Maine FlledSept. 22, 1959, Ser. No. 841,471

3 Claims. (Cl. 200-33) This invention relates to a timing. device, and more particularly, to a time delay mercuryswitch wherein the opening or closing. of an. electrical circuit takes place at a predetermined period after the switch has been actuated.

It is ageneral object of the invention to provide a time delay mercury switch which is instantaneously responsive upon tilting thereof to close a circuit, which requires only a small degree of tilting to set it in operation, "and which is. simple in structure. and inexpensive to manufacture.

A further object is that of devising a switch in which the time delay shall be uniform in all instances.

It. is a more specific object to provide a mercury switch which is comprised of a main body of tubular-form having inserted thereinto a single electrically conductive separator to form a series of compartments with the main body, and which employs a restricted opening or capillary, thereby to minimize the size of. the switch.

Mercury switches of the prior art are in many cases fairly complex in structure employing capsules or containers of unusual shape and design which are not easily fabricated, as they are usually constructed of glass. Those which do not employ a capillary opening for obtaining the delay period by restricting the flow of mercury from one compartment to another are as a result thereof of bulky nature and require a substantial amount of mercury in their operation. Those which have employed a capillary opening often depended upon the weight of a large column of mercury to force a part thereof through the opening, or if they have not, the time delay has been non-uniform or more or less unpredictable.

According to the present invention, the above disadvantages are overcome by providing a switch which includes an outer body of tubular form open at one end into which is inserted a conductive member extending along the major portion of the length of the body to form therewith an upper and a lower compartment, the member having depending side portions to form a narrow passageway in the lower compartment which at one end of the member freely communicates with the upper compartment, a capillary opening being provided in the conductive member at the opposite end thereof for permitting a gradual flow of mercury from the lower to the upper compartment, and a bathe plate extending across the upper compartment adjacent the capillary opening to maintain a portion of the pool of mercury in continuous contact with one side of the capillary opening while at the same time permitting flow of mercury across the top of the plate after the tube has been returned to its normal position.

Additional objects and advantages will be apparent from the description of the invention which follows and by reference to the accompanying figures of drawing, wherein:

Fig. 1 is a front elevation partly in secton of one form of the invention.

Fig. 2 is a sectional view takenon line 2-2 of Fig. 1.

Fig. 3 is a sectional view taken on line 3-3 of Fig. 1.

Fig. 4 is a front elevation of the at-rest position of the mercury switch wherein the circuit is shown as broken between the two electrical contacts.

Fig. 5 showsthe switch in tilted position with the pool of mercury completing the circuit between the contacts.

Fig. 6 is a front elevation of a modified form of the device.

Fig. 7 is a front. elevation of a still further modification.

In Figs. 1 to 5 the novel switch is shown as comprising an outer body portion 10, which is preferably of cylindrical or tubular form closed at one end and open at the other and. is formed of glass or other non-conducting material. Near its openend the-body is provided with a small outwardly-extending cup-shaped portion 11 into which meet the electrical contacts 12 extends and terminates. A conductive member generally denoted by the arrow1'3 and which-may be formed of steel or any other suitable metal is inserted endwise into the opening of the. tubular-body to'form a series of compartments therewith. This member comprises a thin circular end plate 14 and a longitudinally extending portion 15 approximately'centrally located in'the tube to form a first upper compartment 16 and a second lower compartment 17. The longitudinal. portion terminates short of the open end of the tubular body to leave a passageway 18 for the free flow of mercury from the first to the second compartment when the body is tilted to the position indicated in Fig. 5. That portion also includes a pairv of depending side members 19 and 20' which form a seal along the sides of the two compartments and also result in; a. somewhat restricted passageway 21. along the bottom of the major portion of the lower compartment.

A capillary opening or restriction 22 is formed in the portion 15 adjacent the end plate to form a path for retarded flow of mercury from the second to the first compartment after the tube has been tilted and then returned to its normal or at rest position indicated in Fig. 4. A baffle plate 23 extends across the width of the outer body and terminates short of the top of the body as seen in Figs. 1 and 3. This plate serves to maintain a small portion 24 of the larger pool of mercury 25 in continuous contact with the upper end of the capillary opening 30 that mercury will readily flow from the second compartment into the first compartment through that opening and then over the top of the battle plate into the main portion of the upper compartment as soon as the switch is returned to its normal position.

A second electrical contact 26 is fastened by a set screw 27 to any suitable part of the member 13. A cap 28 of an insulating material such as hard rubber serves to seal off the enclosure. The tube is preferably hermetically sealed and filled with hydrogen or other known gases to prevent leakage or oxidation of the mercury.

A modification of the device the electrical contact 12' is inserted through the cap and open end of the tubular body into the passageway 21.

In Fig. 7 the closed end of the outer body is shown as terminating in a flattened portion 29 to shorten further the length of the switch and the second contact 26 is shown as being inserted from the side of the outer body. In this modification the cap has been eliminated and the glass tube has been drawn to a point as shown at 30 and sealed hermetically with hydrogen.

In operation, the switch normally assumes the nonconducting position shown in Fig. 4 wherein contact between the main body of mercury and contact 12 is broken as indicated. The cup-shaped portion 11 will still retain a small portion of mercury even in that position so that the end of the contact 12 is always immersed is seen in Fig. 6 wherein to prevent any point contamination. When the switch 7 is tilted tothe position of Figs. to 7, whatever mercury is contained in the main portion of the upper compartment will readily flow through the substantially large opening 18; into the lower compartment toclose the circuit. However, contact is first made'as the mercury at the lower part flows toward the pool at 11. Since that mercury level stands just below the pool and an appreciable mass of mercury is contained between the contact members 19 and the tube, only a slight motion isneeded to effect the connection. The mercury from the top fills in later.

Then as the switch is returned to the position ofFig. 4, mercury will flow by gravity through the capillary opening and into the first compartment until the level of mercury in the upper and lower compartments is the same, during which time the circuit will again have been opened.

The time delay period may be varied as desired by increasing or decreasing the size of the capillary opening thereby to change the rate at which mercury passes therethrough, by controlling the amount of mercury sealed within the tube, by varying the length of the tube, or

While one embodiment and modifications of the invention have been disclosed, it is to be understood that the inventive concept may be carried out in a number of ways. This invention is, therefore, not to be limited to the precise details described, but is intended to embrace all variations and modifications thereof falling within the spirit of the invention and the scope of the claims.

I claim: s

1. A time delay mercury switch of the delayed opening type which comprises a main tiltable tube of insulating material, -a pool of mercury in said tube, a conductive member extending lengthwise along the major portion of said tube to form a first upper compartment and a second lower compartment therein, said compartments being adapted to communicate freely at one end of said tube, a capillary opening in said conductive member at the opposite end thereof for permitting a gradual flow of mercury from said second compartment upwardly into said-first compartment, a baffle plate extending across by any combination of these. In use the time period I may be varied within limits by increasing or decreasing the degree of tilt of the normal position from the horizontal. Thus the closing of the circuit can be efiected very quickly and without tilting the switch but a few degrees. At breaking contact, due to the construction by which the opening 22 always has a pool of mercury above it with which the mercury below unites when the switch is tiltedto the appropriate angle, a uniform timing of the break at contact 12 or 12 results since apparently,

mercury hesitates to pass through such a small aperture if no mercury is at the other side, but if devised and operated as' herein shown, the entry and flow commences immediately and thus the time interval is always predictable and uniform.

said upper compartment between said opening and said one end of said tube effective to maintain a portion of said pool of mercury in continuous contact with the upper end of said capillary opening while permitting free flowv of mercury across the top of said plate, and a pair of electrical contacts adapted upon tilting of said tube to maintain a closed circuit through said pool of mercury for a predetermined period of time.

. 2. The structure of claim 1 wherein a first of said contacts communicates with said conductive member and the second thereof is adapted to make intermittent contact with said pool of mercury.

3. The structure of claim 1 wherein an insulating cape encloses said tube at said one end.

References Cited in the file of this patent 2,119,944 Mattern June 7, 1938 

